1. Field of the Invention
This invention relates to a method and apparatus for blow molding plastic articles. More particularly, this invention relates to a method and apparatus for blow molding plastic containers by an injection blow molding process.
2. Description of the Prior Art
As is shown, for example, in U.S. Pat. No. 4,239,475 (Rainville), and in U.S. Pat. No. 4,518,549 (Hart), it is known that articles, such as containers, may be manufactured from a suitable thermoplastic material by an injection blow molding process. In such a process, a turret having a plurality of planar, vertically extending faces, usually three (3) such faces, carries a spaced apart plurality of parallel, horizontally extending core rods on each of its faces. The turret is indexed in a horizontal plane about its vertical central axis through a plurality of stations equal in number to the number of faces, with a stop at each station. A preform of the article to be produced, which is usually called a parison, is produced by injection molding on the core rods at the first station, and each such parison is later blown into a container at the second station, after the turret is indexed to advance the parisons to the second station, the blowing being done by injecting compressed air into the parisons at the second station to blow them into contact with blow molds at the second station. The blown containers are then stripped from the core rods at the third station, after the turret is indexed to advance the blown containers to the third station.
It is important that the blown containers be substantially cooled before they are stripped from the core rods at the stripping station. Conventionally, this is done mainly by circulating heated oil through the interiors of the core rods at the injection molding station, the heated oil being at a temperature substantially less than the temperature of the thermoplastic material in the injection molded parisons, for example, at a temperature sufficiently low to bring low density polyethylene parisons at a temperature of approximately 450° F. to a temperature of approximately 200° F. before the parisons are advanced to the blow molding station. However, the use of heated oil as a cooling medium involves a risk that the containers being produced will be contaminated by oil leakage from the core rods; further, the need to initially heat unheated oil, and the need to further cool core rods that are internally heated by the oil passing therethrough, imposes undesired additional cooling loads on the process occurring at the bottle blowing station. Also, the thermal capacitance of hot oil, or any other cooling liquid for that matter, precludes rapid changes in its temperature, even when and if desired for process reasons.
It is to the elimination of the disadvantages of using heated oil or other liquid cooling medium to cool injection molded parisons of articles, especially parisons of containers, which are being manufactured by an injection blow molding machine, that the present invention is directed to.
Accordingly, it is an object of the present invention to provide an improved method and in apparatus for producing articles, especially containers, from a thermoplastic material by an injection blow molding process. It is a further object of the present invention to provide a method and apparatus of the aforesaid character for producing such articles without the need to use a heated oil, or any other cooling liquid, as a cooling medium to cool the articles being produced by injection blow molding.
For a further understanding of the present invention and the objects thereof, attention is directed to the drawing and the following brief description thereof, to the detailed description of the preferred embodiment and to the appended claims.